1. Field of the Invention
The present invention relates to a battery comprising a layered double hydroxide (LDH).
2. Description of the Related Art
Zinc secondary batteries, such as nickel-zinc secondary batteries and zinc-air secondary batteries, have been developed and studied over many years. Unfortunately, these batteries have not yet been put into practice. This is due to a problem that zinc contained in the negative electrode forms dendritic crystals, i.e. dendrites, during a charge mode of the battery and the dendrites break the separator to cause short circuit between the negative electrode and the positive electrode. Thus, a strong demand has arisen for a technique for preventing the short circuit caused by dendritic zinc in zinc secondary batteries, such as nickel-zinc secondary batteries and zinc-air secondary batteries.
In order to meet such a demand, batteries including hydroxide-ion-conductive ceramic separators have been proposed. For example, Patent Document 1 (WO2013/118561) discloses a nickel-zinc secondary battery including a separator composed of a hydroxide-ion-conductive LDH-containing solid electrolyte between a positive electrode and a negative electrode for preventing the short circuit caused by dendritic zinc, wherein the LDH-containing solid electrolyte is a layered double hydroxide (hereinbelow, LDH) having a basic composition represented by the formula: M2+1−xM3+x(OH)2An−x/n·mH2O (wherein M2+ represents at least one type of divalent cation, M3+ represents at least one type of trivalent cation, An− represents an n-valent anion, n is an integer of 1 or more, and x is 0.1 to 0.4). Patent Document 2 (WO2013/073292) discloses a zinc-air secondary battery including a separator composed of an LDH having the same basic composition as that in Patent Document 1 and disposed on one surface of the air electrode for preventing a short circuit caused by dendritic zinc between the positive and negative electrodes during a charge mode of the battery and also preventing the intrusion of carbon dioxide into the electrolytic solution.
Patent Document 3 (WO2013/161516) discloses an application of a hydroxide-ion-conductive ceramic separator to a battery other than a zinc secondary battery; specifically, a lithium-air secondary battery including, as an anion exchanger, an LDH-containing solid electrolyte composed of an LDH having the aforementioned basic composition. According to this patent document, the anion exchanger can prevent the intrusion of carbon dioxide into the battery. Patent Document 4 (WO2014/119665) discloses that an anion-conductive material that may contain an LDH and a polymer is used for a battery component, such as a separator, an electrolyte, or an electrode protectant. According to this patent document, the morphological variation of a zinc electrode active material is reduced if a membrane containing an LDH (e.g., hydrotalcite) and a polymer (e.g., polytetrafluoroethylene) is formed on the zinc-compound-containing electrode through which current flows.
The aforementioned alkaline secondary batteries generally contain an electrolytic solution composed of an aqueous potassium hydroxide (KOH) solution. Techniques for improving the properties of such an electrolytic solution have been proposed. For example, Patent Document 5 (JP2001-500661A) discloses an alkaline storage battery including a zinc negative electrode that is in contact with an electrolytic solution composed of an aqueous KOH solution (initial concentration: 4 to 8 M) containing aluminum (70 to 100 g), wherein the solubility of zinc in the electrolytic solution is controlled through addition of aluminum. The ion-exchange membrane used in Examples described in this patent document is not a ceramic separator, but a hydrocarbon ion-exchange membrane.